Multi-stage optical amplifier and broadband communication system

Abstract

A multi-stage optical amplifier includes an optical fiber with at least a first Raman amplifier fiber and a second Raman amplifier fiber. The optical fiber is configured to be coupled to at least one signal source that produces at least a signal wavelength lambds and at least two pump sources that collectively produce a pump beam of wavelength lambdp. Pump wavelength lambdp is less than signal wavelength lambds. Signal input, signal output and a first pump input port are each coupled to the optical fiber. The first Raman amplifier fiber is positioned between the signal input port and the pump input port. The second Raman amplifier fiber is positioned between the pump input port and signal output port. A second pump input port is coupled to the optical fiber and positioned between the second Raman amplifier fiber and the signal output port. A first lossy member is positioned between the pump input port and the signal output port. The lossy member is lossy in at least one direction so that passage of the pump radiation of wavelength lambdp from the second to the first length of amplifier fiber is substantially blocked. The signal flows in a first direction and the pump beam flows in a reverse direction relative to the first direction.

What is claimed is:  
     
       1. A multi-stage optical amplifier, comprising: 
       an optical fiber including at least a first Raman amplifier fiber and a second Raman amplifier fiber, the optical fiber configured to be coupled to at least one signal source that produces at least a signal wavelength λ s  and at least two pump sources that collectively produce a pump beam of wavelength λ p , wherein pump wavelength λ p  is less than signal wavelength λ s , the first Raman amplifier fiber having an optical noise figure of less than 8 dB and lower noise than the second Raman fiber amplifier, and the second Raman fiber amplifier having a gain level of at least 5 dB;  
       a signal input port coupled to the optical fiber;  
       a signal output port coupled to the optical fiber;  
       a first pump input port, the first Raman amplifier fiber being positioned between the signal input port and the first pump input port and the second Raman amplifier fiber being positioned between the first pump input port and signal output port;  
       a second pump input port coupled to the optical fiber and positioned between the second Raman amplifier fiber and the signal output port; and  
       a first lossy member positioned between the first pump input port and the signal output port, the lossy member being lossy in at least one direction and passage of the pump radiation of wavelength λ p  from the second to the first length of amplifier fiber is substantially blocked; and  
       wherein the signal flows in a first direction and the pump beam flows in a reverse direction relative to the first direction.  
     
     
       2. The multi-stage optical amplifier of  claim 1 , wherein the first pump input port is coupled to a first pump source, and the second pump input port is coupled to a second pump source. 
     
     
       3. The multi-stage optical amplifier of  claim 2 , wherein the first pump source produces a pump beam of wavelength λ p1  and the second pump source produces a pump beam of wavelength λ p2 . 
     
     
       4. The multi-stage optical amplifier of  claim 2  wherein wavelength λ p1  and wavelength λ p2  are the same. 
     
     
       5. The multi-stage optical amplifier of  claim 2  wherein wavelength λ p1  and wavelength λ p2  are different. 
     
     
       6. The multi-stage optical amplifier of  claim 1 , wherein the first and second Raman amplifier fibers have lengths greater than or equal to 200 m. 
     
     
       7. The multi-stage optical amplifier of  claim 1 , wherein pump radiation of wavelength λ p  is in the range of 1300 nm to 1530 nm. 
     
     
       8. The multi-stage optical amplifier of  claim 1 , wherein signal radiation of wavelength λ s  is in the range of 1430 to 1530 nm. 
     
     
       9. The multi-stage optical amplifier of  claim 1 , wherein the first lossy member is an optical isolator. 
     
     
       10. The multi-stage optical amplifier of  claim 1 , wherein the first lossy member is an add/drop multiplexer. 
     
     
       11. The multi-stage optical amplifier of  claim 1 , wherein the first lossy member is a gain equalization member. 
     
     
       12. The multi-stage optical amplifier of  claim 1 , wherein the first lossy member is a dispersion compensation element. 
     
     
       13. The multi-stage optical amplifier of  claim 1 , further comprising: 
       at least one WDM coupler to couple a pump path from the signal input port to the signal output port.  
     
     
       14. The multi-stage optical amplifier of  claim 1 , wherein at least one of the first and second Raman amplifier fibers is a dispersion compensating fiber. 
     
     
       15. The multi-stage optical amplifier of  claim 1 , wherein the first and second Raman amplifier fibers are each dispersion compensating fibers. 
     
     
       16. The multi-stage optical amplifier of  claim 1 , wherein the optical fiber includes a third Raman amplifier fiber. 
     
     
       17. The multi-stage optical amplifier of  claim 16 , further comprising: a third pump source coupled to the third Raman amplifier fiber. 
     
     
       18. The multi-stage optical amplifier of  claim 17 , wherein the optical fiber includes a third Raman amplifier fiber. 
     
     
       19. The multi-stage optical amplifier of  claim 18 , further comprising: 
       a fourth pump source coupled to the fourth Raman amplifier fiber.  
     
     
       20. The multi-stage optical amplifier of  claim 17 , wherein each of the first, second and third pump sources is a laser diode pump source. 
     
     
       21. The multi-stage optical amplifier of  claim 19 , wherein each of the first, second, third and fourth pump sources is a laser diode pump source. 
     
     
       22. A broadband booster amplifier, comprising: 
       a plurality of transmitters transmitting a plurality of wavelengths;  
       a combiner coupled to the plurality of transmitters;  
       an optical fiber coupled to the combiner, the optical fiber including at least a first Raman amplifier fiber and a second Raman amplifier fiber, the optical fiber configured to be coupled to at least one signal source and at least two pump sources, the first Raman fiber amplifier having an optical noise figure of less than 8 dB and lower noise than the second Raman fiber amplifier, and the second Raman fiber amplifier having a gain level of at least 5 dB;  
       a signal input port coupled to the optical fiber;  
       a signal output port coupled to the optical fiber, wherein a signal introduced through the signal input port propagates from the first stage amplifier to the second stage amplifier;  
       a first pump input port, the first Raman amplifier fiber being positioned between the signal input port and the first pump input port and the second Raman amplifier fiber being positioned between the first pump input port and signal output port;  
       a second pump input port coupled to the optical fiber and positioned between the second Raman amplifier fiber and the signal output port;  
       a first lossy member positioned between the first pump input port and the signal output port, wherein the lossy member is lossy in at least one direction and passage of the pump radiation from the second to the first length of amplifier fiber is substantially blocked; and  
       wherein the signal flows in a first direction and the pump beam flows in a reverse direction relative to the first direction.  
     
     
       23. A broadband pre-amplifier, comprising: 
       an optical fiber including at least a first Raman amplifier fiber and a second Raman amplifier fiber, the optical fiber configured to be coupled to at least one signal source and at least two pump sources, the first Raman fiber amplifier having an optical noise figure of less than 8 dB and lower noise than the second Raman fiber amplifier, and the second Raman fiber amplifier having a gain level of at least 5 dB;  
       a signal input port coupled to the optical fiber;  
       a signal output port coupled to the optical fiber;  
       a first pump input port, the first Raman amplifier fiber being positioned between the signal input port and the first pump input port and the second Raman amplifier fiber being positioned between the first pump input port and signal output port;  
       a second pump input port coupled to the optical fiber and positioned between the second Raman amplifier fiber and the signal output port;  
       a first lossy member positioned between the first pump input port and the signal output port, wherein the lossy member is lossy in at least one direction and passage of pump radiation from the second to the first length of amplifier fiber is substantially blocked;  
       a splitter coupled to the signal output port;  
       a plurality of receivers coupled to the splitter; and  
       wherein the signal flows in a first direction and the pump beam flows in a reverse direction relative to the first direction.  
     
     
       24. A broadband communication system, comprising: 
       a transmitter;  
       an optical fiber coupled to the transmitter, the optical fiber including at least a first Raman amplifier fiber and a second Raman amplifier fiber, the optical fiber configured to be coupled to at least one signal and at least two pump sources, the first Raman fiber amplifier having an optical noise figure of less than 8 dB and lower noise than the second Raman fiber amplifier, and the second Raman fiber amplifier having a gain level of at least 5 dB;  
       a signal input port coupled to the optical fiber;  
       a signal output port coupled to the optical fiber;  
       a first pump input port, the first Raman amplifier fiber being positioned between the signal input port and the first pump input port and the second Raman amplifier fiber being positioned between the first pump input port and signal output port;  
       a second pump input port coupled to the optical fiber and positioned between the second Raman amplifier fiber and the signal output port; and  
       a first lossy member positioned between the first pump input port and the signal output port, wherein the lossy member is lossy in at least one direction and passage of pump radiation of from the second to the first length of amplifier fiber is substantially blocked;  
       a receiver coupled to the optical fiber; and  
       wherein the signal flows in a first direction and the pump beam flows in a reverse direction relative to the first direction.  
     
     
       25. The system of  claim 24 , wherein the first pump input port is coupled to a first pump source, and the second pump input port is coupled to a second pump source. 
     
     
       26. The system of  claim 25 , wherein the first pump source produces a pump beam of wavelength λ p1  and the second pump source produces a pump beam of wavelength λ p2 . 
     
     
       27. The system of  claim 25  wherein wavelength λ p1  and wavelength λ p2  are the same. 
     
     
       28. The system of  claim 25  wherein wavelength λ p1  and wavelength λ p2  are different. 
     
     
       29. The system of  claim 24 , wherein the first and second Raman amplifier fibers have lengths greater than or equal to 200 m. 
     
     
       30. The system of  claim 24 , wherein pump radiation of wavelength λ p  is in the range of 1300 nm to 1530 nm. 
     
     
       31. The system of  claim 24 , wherein signal radiation of wavelength λ s  is in the range of 1430 to 1530 nm. 
     
     
       32. The system of  claim 24 , wherein the first lossy member is an optical isolator. 
     
     
       33. The system of  claim 24 , wherein the first lossy member is an add/drop multiplexer. 
     
     
       34. The system of  claim 24 , wherein the first lossy member is a gain equalization member. 
     
     
       35. The system of  claim 24 , wherein the first lossy member is a dispersion compensation element. 
     
     
       36. The system of  claim 24 , further comprising: 
       at least one WDM coupler to couple a pump path from the signal input port to the signal output port.  
     
     
       37. The system of  claim 24 , wherein at least one of the first and second Raman amplifier fibers is a dispersion compensating fiber. 
     
     
       38. The system of  claim 24 , wherein the first and Raman amplifier fibers are each dispersion compensating fibers. 
     
     
       39. The system of  claim 24 , wherein the optical fiber includes a third Raman amplifier fiber. 
     
     
       40. The system of  claim 39 , further comprising: 
       a third pump source coupled to the third Raman amplifier fiber.  
     
     
       41. The system of  claim 40 , wherein the optical fiber includes a fourth Raman amplifier fiber. 
     
     
       42. The system of  claim 41 , further comprising: 
       a fourth pump source coupled to the fourth Raman amplifier fiber.  
     
     
       43. The system of  claim 40 , wherein each of the first, second and third pump sources is a laser diode pump source. 
     
     
       44. The system of  claim 42 , wherein each of the first, second, third and fourth pump sources is a laser diode pump source. 
     
     
       45. A broadband communication system, comprising: 
       a transmitter;  
       an optical fiber coupled to the transmitter, the optical fiber including at least a first Raman amplifier fiber and a second Raman amplifier fiber, the optical fiber configured to be coupled to at least one signal source and at least two pump sources, the first Raman fiber amplifier having an optical noise figure of less than 8 dB and lower noise than the second Raman fiber amplifier, and the second Raman fiber amplifier having a gain level of at least 5 dB;  
       a signal input port coupled to the optical fiber;  
       a signal output port coupled to the optical fiber;  
       a first pump input port, the first Raman amplifier fiber being positioned between the signal input port and the first pump input port and the second Raman amplifier fiber being positioned between the first pump input port and signal output port;  
       a second pump input port coupled to the optical fiber and positioned between the second Raman amplifier fiber and the signal output port; and  
       a first lossy member positioned between the first pump input port and the signal output port, wherein the lossy member is lossy in at least one direction and passage of pump radiation from the second to the first length of amplifier fiber is substantially blocked;  
       at least one in-line broadband amplifier coupled to the optical fiber;  
       a receiver coupled to the in-line broadband amplifier; and  
       wherein the signal flows in a first direction and the pump beam flows in a reverse direction relative to the first direction.  
     
     
       46. The system of  claim 45 , wherein the in-line broadband amplifier comprises: 
       an optical fiber including at least a first Raman amplifier fiber and a second Raman amplifier fiber, the optical fiber configured to be coupled to at least one signal source and at least two pump sources;  
       a signal input port coupled to the optical fiber;  
       a signal output port coupled to the optical fiber;  
       a first pump input port, the first Raman amplifier fiber being positioned between the signal input port and the pump input port and the second Raman amplifier fiber being positioned between the pump input port and signal output port;  
       a second pump input port coupled to the optical fiber and positioned between the second Raman amplifier fiber and the signal output port; and  
       a first lossy member positioned between the pump input port and the signal output port, wherein the lossy member is lossy in at least one direction and passage of pump radiation from the second to the first length of amplifier fiber is substantially blocked and  
       wherein the signal flows in a first direction and the pump beam flows in a reverse direction relative to the first direction.  
     
     
       47. A broadband communication system, comprising: 
       a transmitter;  
       a broadband booster amplifier;  
       an optical fiber coupled to the broadband booster amplifier, the optical fiber including at least a first Raman amplifier fiber and a second Raman amplifier fiber, the optical fiber configured to be coupled to at least one signal and at least two pump sources, the first Raman fiber amplifier having an optical noise figure of less than 8 dB and lower noise than the second Raman fiber amplifier, and the second Raman fiber amplifier having a gain level of at least 5 dB;  
       a signal input port coupled to the optical fiber;  
       a signal output port coupled to the optical fiber;  
       a first pump input port, the first Raman amplifier fiber being positioned between the signal input port and the first pump input port and the second Raman amplifier fiber being positioned between the first pump input port and signal output port;  
       a second pump input port coupled to the optical fiber and positioned between the second Raman amplifier fiber and the signal output port; and  
       a first lossy member positioned between the first pump input port and the signal output port, wherein the lossy member is lossy in at least one direction and passage of pump radiation of from the second to the first length of amplifier fiber is substantially blocked;  
       a receiver coupled to the optical fiber; and  
       wherein the signal flows in a first direction and the pump beam flows in a reverse direction relative to the first direction.  
     
     
       48. The system of  claim 47 , wherein the broadband booster amplifier comprises: 
       a plurality of transmitters transmitting a plurality of wavelengths;  
       a combiner coupled to the plurality of transmitters;  
       an optical fiber coupled to the combiner, the optical fiber including at least a first Raman amplifier fiber and a second Raman amplifier fiber, the optical fiber configured to be coupled to at least one signal source and at least two pump sources;  
       a signal input port coupled to the optical fiber;  
       a signal output port coupled to the optical fiber, wherein a signal introduced through the signal input port propagates from the first stage amplifier to the second stage amplifier;  
       a first pump input port, the first Raman amplifier fiber being positioned between the signal input port and the pump input port and the second Raman amplifier fiber being positioned between the pump input port and signal output port;  
       a second pump input port coupled to the optical fiber and positioned between the second Raman amplifier fiber and the signal output port;  
       a first lossy member positioned between the pump input port and the signal output port, wherein the lossy member is lossy in at least one direction and passage of the pump radiation from the second to the first length of amplifier fiber is substantially blocked; and  
       wherein the signal flows in a first direction and the pump beam flows in a reverse direction relative to the first direction.  
     
     
       49. A broadband communication system, comprising: 
       a transmitter;  
       an optical fiber coupled to the transmitter, the optical fiber including at least a first Raman amplifier fiber and a second Raman amplifier fiber, the optical fiber configured to be coupled to at least one signal source and at least two pump sources, the first Raman fiber amplifier having an optical noise figure of less than 8 dB and lower noise than the second Raman fiber amplifier, and the second Raman fiber amplifier having a gain level of at least 5 dB;  
       a signal input port coupled to the optical fiber;  
       a signal output port coupled to the optical fiber;  
       a first pump input port, the first Raman amplifier fiber being positioned between the signal input port and the first pump input port and the second Raman amplifier fiber being positioned between the first pump input port and signal output port;  
       a second pump input port coupled to the optical fiber and positioned between the second Raman amplifier fiber and the signal output port;  
       a first lossy member positioned between the first pump input port and the signal output port, wherein the lossy member is lossy in at least one direction and passage of pump radiation from the second to the first length of amplifier fiber is substantially blocked;  
       a broadband pre-amplifier coupled to the optical fiber;  
       a receiver coupled to the broadband pre-amplifier; and  
       wherein the signal flows in a first direction and the pump beam flows in a reverse direction relative to the first direction.  
     
     
       50. The system of  claim 49 , wherein the broadband pre-amplifier comprises: 
       an optical fiber including at least a first Raman amplifier fiber and a second Raman amplifier fiber, the optical fiber configured to be coupled to at least one signal source and at least two pump sources;  
       a signal input port coupled to the optical fiber;  
       a signal output port coupled to the optical fiber;  
       a first pump input port, the first Raman amplifier fiber being positioned between the signal input port and the pump input port and the second Raman amplifier fiber being positioned between the pump input port and signal output port;  
       a second pump input port coupled to the optical fiber and positioned between the second Raman amplifier fiber and the signal output port;  
       a first lossy member positioned between the pump input port and the signal output port, wherein the lossy member is lossy in at least one direction and passage of pump radiation from the second to the first length of amplifier fiber is substantially blocked;  
       a splitter coupled to the signal output port;  
       a plurality of receivers coupled to the splitter; and  
       wherein the signal flows in a first direction and the pump beam flows in a reverse direction relative to the first direction.  
     
     
       51. A broadband communication system, comprising: 
       a transmitter;  
       a booster broadband amplifier coupled to the transmitter;  
       an optical fiber coupled to the broadband booster amplifier, the optical fiber including at least a first Raman amplifier fiber and a second Raman amplifier fiber, the optical fiber configured to be coupled to at least one signal source and at least two pump sources, the first Raman fiber amplifier having an optical noise figure of less than 8 dB and lower noise than the second Raman fiber amplifier, and the second Raman fiber amplifier having a gain level of at least 5 dB;  
       a signal input port coupled to the optical fiber;  
       a signal output port coupled to the optical fiber;  
       a first pump input port, the first Raman amplifier fiber being positioned between the signal input port and the first pump input port and the second Raman amplifier fiber being positioned between the first pump input port and signal output port;  
       a second pump input port coupled to the optical fiber and positioned between the second Raman amplifier fiber and the signal output port;  
       a first lossy member positioned between the first pump input port and the signal output port, wherein the lossy member is lossy in at least one direction and passage of pump radiation from the second to the first length of amplifier fiber is substantially blocked;  
       a broadband pre-amplifier coupled to the optical fiber;  
       a receiver coupled to the broadband pre-amplifier; and  
       wherein the signal flows in a first direction and the pump beam flows in a reverse direction relative to the first direction.  
     
     
       52. The system of  claim 51 , wherein the broadband booster amplifier comprises: 
       a plurality of transmitters transmitting a plurality of wavelengths;  
       a combiner coupled to the plurality of transmitters;  
       an optical fiber coupled to the combiner, the optical fiber including at least a first Raman amplifier fiber and a second Raman amplifier fiber, the optical fiber configured to be coupled to at least one signal source and at least two pump sources;  
       a signal input port coupled to the optical fiber;  
       a signal output port coupled to the optical fiber, wherein a signal introduced through the signal input port propagates from the first stage amplifier to the second stage amplifier;  
       a first pump input port, the first Raman amplifier fiber being positioned between the signal input port and the pump input port and the second Raman amplifier fiber being positioned between the pump input port and signal output port;  
       a second pump input port coupled to the optical fiber and positioned between the second Raman amplifier fiber and the signal output port;  
       a first lossy member positioned between the pump input port and the signal output port, wherein the lossy member is lossy in at least one direction and passage of the pump radiation from the second to the first length of amplifier fiber is substantially blocked; and  
       wherein the signal flows in a first direction and the pump beam flows in a reverse direction relative to the first direction.  
     
     
       53. The system of  claim 52 , wherein the broadband pre-amplifier comprises: 
       an optical fiber including at least a first Raman amplifier fiber and a second Raman amplifier fiber, the optical fiber configured to be coupled to at least one signal source and at least two pump sources;  
       a signal input port coupled to the optical fiber;  
       a signal output port coupled to the optical fiber;  
       a first pump input port, the first Raman amplifier fiber being positioned between the signal input port and the pump input port and the second Raman amplifier fiber being positioned between the pump input port and signal output port;  
       a second pump input port coupled to the optical fiber and positioned between the second Raman amplifier fiber and the signal output port;  
       a first lossy member positioned between the pump input port and the signal output port, wherein the lossy member is lossy in at least one direction and passage of pump radiation from the second to the first length of amplifier fiber is substantially blocked;  
       a splitter coupled to the signal output port;  
       a plurality of receivers coupled to the splitter; and  
       wherein the signal flows in a first direction and the pump beam flows in a reverse direction relative to the first direction.  
     
     
       54. A multi-stage optical amplifier, comprising: 
       an optical fiber including at least a distributed Raman amplifier fiber and a discrete Raman amplifier fiber, the optical fiber configured to be coupled to at least one signal source that produces at least a signal wavelength λ s  and at least two pump sources that collectively produce a pump beam of wavelength λ p , wherein pump wavelength λ p  is less than signal wavelength λ s , the first Raman fiber amplifier having an optical noise figure of less than 8 dB and lower noise than the second Raman fiber amplifier, and the second Raman fiber amplifier having a gain level of at least 5 dB;  
       a signal input port coupled to the optical fiber;  
       a signal output port coupled to the optical fiber;  
       a first pump input port, the distributed Raman amplifier fiber being positioned between the signal input port and the first pump input port and the discrete Raman amplifier fiber being positioned between the first pump input port and signal output port;  
       a second pump input port coupled to the optical fiber and positioned between the discrete Raman amplifier fiber and the signal output port; and  
       wherein the signal flows in a first direction and the pump beam flows in a reverse direction relative to the first direction.  
     
     
       55. The multi-stage optical amplifier of  claim 54 , wherein the first pump input port is coupled to a first pump source, and the second pump input port is coupled to a second pump source. 
     
     
       56. The multi-stage optical amplifier of  claim 55 , wherein the first pump source produces a pump beam of wavelength λ p1  and the second pump source produces a pump beam of wavelength λ p2 . 
     
     
       57. The multi-stage optical amplifier of  claim 55  wherein wavelength λ p1  and wavelength λ p2  are the same. 
     
     
       58. The multi-stage optical amplifier of  claim 55  wherein wavelength λ p1  and wavelength λ p2  are different. 
     
     
       59. The multi-stage optical amplifier of  claim 55 , wherein the distributed and discrete Raman amplifier fibers have lengths greater than or equal to 200 m. 
     
     
       60. The multi-stage optical amplifier of  claim 54 , wherein pump radiation of wavelength λ p  is in the range of 1300 nm to 1530 nm. 
     
     
       61. The multi-stage optical amplifier of  claim 54 , wherein signal radiation of wavelength λ s  is in the range of 1430 to 1530 nm. 
     
     
       62. The multi-stage optical amplifier of  claim 54 , further comprising: 
       at least one WDM coupler to couple a pump path from the signal input port to the signal output port.  
     
     
       63. The multi-stage optical amplifier of  claim 54 , wherein at least one of the distributed and discrete Raman amplifier fibers is a dispersion compensating fiber. 
     
     
       64. The multi-stage optical amplifier of  claim 54 , wherein the distributed and discrete Raman amplifier fibers are each dispersion compensating fibers. 
     
     
       65. The multistage optical amplifier of  claim 54 , wherein the optical fiber includes a third Raman amplifier fiber. 
     
     
       66. The multi-stage optical amplifier of  claim 65 , further comprising: 
       a third pump source coupled to the third Raman amplifier fiber.  
     
     
       67. The multi-stage optical amplifier of  claim 66 , wherein the optical fiber includes a fourth Raman amplifier fiber. 
     
     
       68. The multi-stage optical amplifier of  claim 55 , wherein each of the first and second pump sources is a laser diode pump source.